kexec: Add option to get crash kernel region size

Crash kernel region size is available via sysfs on Linux running on
bare metal. However, this does not work when Linux runs as Xen dom0.
In this case Xen crash kernel region size should be established using
__HYPERVISOR_kexec_op hypercall (Linux kernel kexec functionality does
not make a lot of sense in Xen dom0). Sadly hypercalls are not easily
accessible using shell scripts or something like that. Potentially we
can check "xl dmesg" output for crashkernel option but this is not nice.
So, let's add this functionality, for Linux running on bare metal and
as Xen dom0, to kexec-tools. This way kdump scripts may establish crash
kernel region size in one way regardless of platform. All burden of
platform detection lies on kexec-tools.

Figure (and unit) displayed by this new kexec-tools functionality is
the same as one taken from /sys/kernel/kexec_crash_size.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

1 files changed, 16 insertions, 0 deletions

diff --git a/kexec/kexec.c b/kexec/kexec.c
index a2ba79d..cfd837c 100644
--- a/kexec/kexec.c
+++ b/kexec/kexec.c
@@ -995,6 +995,7 @@ void usage(void)
 	       "     --mem-max=<addr> Specify the highest memory address to\n"
 	       "                      load code into.\n"
 	       "     --reuseinitrd    Reuse initrd from first boot.\n"
+	       "     --print-ckr-size Print crash kernel region size.\n"
 	       "     --load-preserve-context Load the new kernel and preserve\n"
 	       "                      context of current kernel during kexec.\n"
 	       "     --load-jump-back-helper Load a helper image to jump back\n"
@@ -1218,6 +1219,18 @@ static int do_kexec_file_load(int fileind, int argc, char **argv,
 	return ret;
 }
 
+static void print_crashkernel_region_size(void)
+{
+	uint64_t start = 0, end = 0;
+
+	if (is_crashkernel_mem_reserved() &&
+	    get_crash_kernel_load_range(&start, &end)) {
+		fprintf(stderr, "get_crash_kernel_load_range() failed.\n");
+		return;
+	}
+
+	printf("%lu\n", (start != end) ? (end - start + 1) : 0UL);
+}
 
 int main(int argc, char *argv[])
 {
@@ -1375,6 +1388,9 @@ int main(int argc, char *argv[])
 		case OPT_STATUS:
 			do_status = 1;
 			break;
+		case OPT_PRINT_CKR_SIZE:
+			print_crashkernel_region_size();
+			return 0;
 		default:
 			break;
 		}